1. Field of the Invention
The present invention generally relates to magnetic sensing elements for use in magnetic sensors and hard disks and methods for making the same. In particular, it relates to a magnetic sensing element that can be readily used with narrower tracks and that has improved sensitivity to magnetic fields, and to a method for making the same.
2. Description of the Related Art
FIG. 24 is a cross-sectional view of a conventional spin-valve magnetic sensing element viewed from a face that opposes a recording medium. Hereinafter, this face is referred to as the “opposing face”.
The magnetic sensing element includes a composite film 9 constituted from an antiferromagnetic layer 2, a pinned magnetic layer 3, a nonmagnetic material layer 4, a free magnetic layer 5, a nonmagnetic material layer 6, a pinned magnetic layer 7, and an antiferromagnetic layer 8; an electrode layer 1 at the bottom of the composite film 9; an electrode layer 10 at the top of the composite film 9; hard bias layers 11 at the two sides of the free magnetic layer 5; insulating layers 12 formed at the bottom of the hard bias layers 11; and insulating layers 13 formed at the top of the hard bias layers 11.
The antiferromagnetic layers 2 and 8, the pinned magnetic layers 3 and 7, and the free magnetic layer 5 are composed of a ferromagnetic material such as NiFe. The nonmagnetic material layers 4 and 6 are composed of copper. The hard bias layers 11 are composed of a hard magnetic material such as CoPt. The insulating layers 12 and 13 are composed of alumina. The electrode layers 1 and 10 are composed of a conductive material such as chromium.
In the magnetic sensing element shown in FIG. 24, the nonmagnetic material layer 4 and the pinned magnetic layer 3 are disposed under the free magnetic layer 5, and the nonmagnetic material layer 6 and the pinned magnetic layer 7 are disposed above the free magnetic layer 5. Such a structure is called a “dual spin-valve magnetic sensing element”. The dual spin-valve magnetic sensing element detects a magnetic field recorded on a recording medium such as a hard disk.
The magnetic sensing element shown in FIG. 24 is of a current-perpendicular-to-the-plane (CCP) type in which an electric current flows perpendicular to the surface of each layer of the composite film 9.
The magnetization directions of the pinned magnetic layers 3 and 7 are pinned in the Y direction in the drawing. The free magnetic layer 5 is put into a single-magnetic-domain state in the track width direction (the X direction in the drawing) by longitudinal bias magnetic fields from the hard bias layers 11 when no external magnetic field is applied. The magnetization direction of the free magnetic layer 5 changes by application of an external magnetic field, resulting in a change in electrical resistance of the composite film 9. The change in electrical resistance is output as a change in voltage or current to detect the external magnetic field.
The composite film 9 of the magnetic sensing element shown in FIG. 24 has two side faces 9a. Each of the side faces 9a is a continuous slope.
The magnetic sensing element having the composite film 9 of such a structure has the following drawbacks during the fabrication process.
FIGS. 25 to 27 are cross-sectional views showing the steps of making the magnetic sensing element shown in FIG. 24.
Referring to FIG. 25, solid layers of the antiferromagnetic layer 2, the pinned magnetic layer 3, the nonmagnetic material layer 4, the free magnetic layer 5, the nonmagnetic material layer 6, the pinned magnetic layer 7, and the antiferromagnetic layer 8 are deposited on the electrode layer 1 to form the composite film 9.
The composite film 9 is annealed in a magnetic field (field annealing) to generate exchange coupling magnetic fields in the Y direction between the antiferromagnetic layer 2 and the pinned magnetic layer 3 and between the antiferromagnetic layer 8 and the pinned magnetic layer 7. Subsequently, a resist layer R1 having a predetermined length in the track width direction is formed on the antiferromagnetic layer 8.
In the step shown in FIG. 26, the two side portions of the composite film 9 not covered by the resist layer R1 is removed by ion milling or reactive ion etching (RIE).
In an actual fabrication process, the material of the composite film 9 redeposits on the side faces 9a of the remaining portion of the composite film 9 to form redeposition layers A, as shown in FIG. 26. Since the thickness T of the antiferromagnetic layers 2 and 8 is large, i.e., approximately 200 Å, significant amounts materials of these layers redeposit on the composite film 9.
The redeposition layers A causes short-circuiting between the pinned magnetic layer 3 and the free magnetic layer 5 and between the pinned magnetic layer 7 and the free magnetic layer 5 and thereby decreases the magnetic detection outputs. Moreover, the redeposition layers A hinder the reduction in track width of the magnetic sensing element. Furthermore, the redeposition layers A degrade the quality of the magnetic sensing element.
The materials of the composite film 9 also redeposit on the side faces of the resist layer R1 to form redeposition layers B.
The redeposition layers B degrade accuracy of positioning the hard bias layers 11 during the deposition of the insulating layers 12, the hard bias layers 11, and the insulating layers 13 by sputtering using the resist layer R1 as a mask. Moreover, the resist layer R1 is difficult to remove.
In other words, the hard bias layers 11 do not come precisely at the two sides of the free magnetic layer 5 in the track width direction and may be shifted in the Z direction in the drawing. Moreover, the distance between the free magnetic layer 5 and each of the hard bias layers 11 may increase. These will result in a decrease in the magnetic detection outputs and poor in asymmetry of the output since the longitudinal bias magnetic fields cannot be stably supplied to the free magnetic layer 5.